The present invention relates to an optical information recording and reproducing system for recording or reproducing information by irradiating with a laser beam, and, more particularly, to an optical information recording and reproducing system for dealing in a unified manner with defective sectors of a write type optical disk and a read only type optical disk.
A read only type optical disk (hereinafter referred to as RO optical disk), in which data are recorded on a disk-shaped plastic base material in the form of concave and convex pits of a submicron order and the data are reproduced by a laser beam, and further a write type optical disk (hereinafter referred to as WT disk), in which data can be recorded like a magnetic disk, are receiving attention.
In these disks, code data are recorded or reproduced on a sector unit basis to serve as an external storage device for a personal computer or the like. In particular, there is a demand for an optical information recording and reproducing system of a multidisk type having compatibility which makes it possible for the RO optical disk, from which a large amount of data can be reproduced at low cost, and the WT disk, on which a user can freely record data, to be reproduced or to be recorded and reproduced, respectively, by the same apparatus.
In an optical disk, data are recorded and reproduced by irradiating it with a laser beam which has been converged to have a diameter of about 1 .mu.m. Therefore, various kinds of data errors are caused by dust on a surface of the disk, impurity substances in a base material of the disk, defects on the recording surface and the like. In order to correct and detect such data errors, in an optical disk having a sector structure, an encoding process to detect and correct errors is applied to data on a sector unit basis, thereby causing data in each sector to be correctly reproduced. However, since the error detection/correction code employs sectors of 512 bytes to 2 kilo bytes as a unit it is difficult to provide a sufficient interleaving length therefore as can be done in a compact disc (CD) having no sector structure. If a long form of error extending to occupy the whole area of a sector occurs, these errors cannot be corrected, so that it becomes difficult to perform proper data reproduction.
Therefore, in a WT disk, immediately after data have been recorded thereon, a read verification process is performed, in which data are reproduced and a check is made to see if the recorded data are accurately reproduced or not. When defective sectors are detected by the read verification process, alternating processing is performed, in which the defective sectors are recorded in alternate sectors provided in a special area on the optical disk. However, there have been several problems in the WT disk such that, because defects of the optical disk increase due to the median life or an increase in the number of repetitive recording times, it becomes complex and difficult to manage the alternate sectors and also the alternating processing time becomes long.
On the other hand, since a large number of duplicates of the RO optical disk are produced by a stamping method in a special factory, the foregoing read verification process cannot be used there. Therefore, the quality control of data is performed by reading data from all the disks produced, by checking the read-out data to find out defective disks and by destroying such defective disks which have been found. However, such total inspection (or 100% inspection) as mentioned above gives rise to a problem of an increase in manufacturing cost.